Antioxidative Properties and Interconversion of tert-Butylhydroquinone and tert-Butylquinone in Soybean Oils.

During the process of antioxidation of tert-butylhydroquinone (TBHQ) in oil and fat systems, tert-butylquinone (TQ) can be formed, which has higher toxicity than TBHQ. The changes of TBHQ and TQ in edible oils at room temperature (RT) or under thermal treatment were investigated. Under thermal treatment, volatilization was the main pathway of TBHQ loss in edible oils. TQ was the main oxidation product of TBHQ under thermal treatment as well as at RT. The amount of TQ in thermally treated oils was much less than that in oils stored at RT due to the decreased amount of oxygen dissolved in oils and easy volatilization of TQ at high temperature. In addition, TQ can be reduced to TBHQ by reduction components in edible oils, but the conversion amount was very small. Thus, TQ, theoretically having no antioxidative property, presented a very weak antioxidative activity equivalent to that of BHA due to the presence of insignificant amount of TBHQ formed from TQ in edible oils. The narrow potential difference of 0.059 between oxidation and reduction peaks of TBHQ and TQ resulted in easy interconversion of TBHQ and TQ under the action of common oxidation and reduction substances which have a higher oxidation potential or a lower reduction potential than they have.